Musical instrument tuning reference standard

ABSTRACT

A reference standard for supplying E at 330 Hz. for tuning a guitar or similar instrument. This is accomplished by taking the standard 60 Hz. powerline frequency, dividing it by two to get a 30 Hz. fundamental with odd harmonics and isolating the 11the harmonic by dynamic filtration. The final signal has the desirable range of harmonics accompanying the 330 Hz. fundamental. Variations are shown, including adapting the system for operation on 50 Hz. powerline frequency.

United States Patent 1 1 3,585,898

[72] Inventor Peter-Davidson [56] ReferencesCited IN m UNITED STATESPATENTS gm" n mo 2,901,699 8/1959 Motzetal 324/78 45] rammed 3,383,4525/1968 Parketal.... 84/].ll m] cc m on 3,412,116 10/1969 Schott 34/4543,501,992 3/1970 Osbornetal. 84/454 Primary Examiner-Richard B.Wilkinson Assistant Examiner-Lawrence R. Franklin Anomey-Gradolph, Love,Rogers and Van Sciver [54] MUSICAL TUNING EFERENCE ABSTRACT: A referencestandard for supplying E at'330 Hz.

STANDARD 7 for tunmg a guitar or s milar lnstrument. This isaccomplished 4 8* I by taking the standard 60 Hz. powerline frequency,dividing it [52] US. Cl 84/454, by two to get a 30 Hz. fundamental withodd harmonics and 84/l .01, 84/DlG. 18 307/260 isolating the lltheharmonic by dynamic filtration. The final 5 I] lit. CL. G10 7/02signal-has the desirable range of harmonic: accompanying the (50] FieldolSareh 84/ l .01, 330 Hz. fundamental. Variations are shown, includingadapt- L] l, 1.19, 4545307/260; 340/384 E ing the system for'ope'rationon 50 Hz. powerline frequency.

6 19 I l -{8 J8 lgg 20 4, 4 1' 33. 74 44 a; ,64 /76 K I xAI 9; 102

MUSICAL INSTRUMENT TUNING REFERENCE STANDARD BACKGROUND OF THEINVENTION 1. Field of the Invention Tuning reference standards fortunable musical instruments such as guitars, for instance.

2. Description of the Prior Art In the past many different types oftuning reference standards have been employed or suggested. Those mostcustomarily used are other musical instruments of fixed pitch, pianos ororgans, for instance, if they are present, or such portable devices aspitch pipes or tuning forks. Electronic oscillators have also been used,but are rather expensive if sufficie ntly precise. Just what note thestandard is supplied for is not particularly important, but for a guitaror other fretted instrument it is preferable if the standard is suchthat one of the strings can be adjusted to zero beat therewith when thestring is open, that is, when the string is not pressed against any ofthe frets.

SUMMARY OF THE INVENTION At present one of the most popular tunableinstruments is the electronically amplified guitar. This suggests thatit would be an advantage to supply some sort of electronic tuningreference standard in connection with the amplifier, if this could bedone at reasonable expense considering the precision required.Investigation of the problem disclosed to the applicant that the Estring theoretically should be tuned to 329.6 Hz. when open nonfretted).It also appeared that a reliable ultimate standard frequency generallyavailable is the 60 Hz. powerline frequency. This ordinarily is held at60 Hz. to within 0.66 Hz. line drift by the power companies and formusical purposes may be considered as nonvariable. The applicant alsoappreciated that if one took the line frequency of 60 Hz. and divided itby two with an ordinary flip-flop circuit, the result would be a 30 Hz.square wave, which comprises a fundamental accompanied by a decliningseries of odd harmonies. By proper filtration the eleventh harmonic ofthis 30 Hz. wave could be selected and by appropriate wave shaping, adeclining series of harmonics could. be added thereto, thereby giving acomplex wave, with its fundamental at 330 Hz. This is only 0.4 Hz.removed from the theoretical E at 329.6 Hz. The total possible errorincluding the line frequency drift using this approach is, therefore,one-half 0.66 Hz. (possible line drift) +0.4 Hz. or 0.73 Hz. or 0.22percent. This is well within acceptable limits and for practicalpurposes can be assumed to be accurate.

' Although circuitry is given hereafter, to accomplish the above, andthere may be some specific novelty therein, it is stressed that manydifferent circuit arrangements will occur to those skilled in the artfor accomplishing the purpose. The invention, therefore, is believed toreside largely in the realization that the eleventh harmonic of one-halfthe 60 Hz. line frequency is the E string frequency of a guitar.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I of the drawing is a circuitdiagram of mechanism for practicing the invention;

FIG. 2 is a diagram of a variation thereof;

FIG. 3 illustrates an adaptation of the circuit of FIG. 1 to 50 Hz.; and

FIG. 4 illustrates a variation which adapts the circuit of FIG. 1 toboth 60 Hz. and 50 Hz.

DESCRIPTION OF THE PREFERRED EMBODIMENT The 60 Hz. line frequency isapplied at terminal which is connected to the junction of the cathodeend of diode l5 and the base of transistor 12 through resistor 14. Theanode end of diode 15 is connected to ground. Therefore, the positiveside of the rectified 60 Hz. frequency appears at the base of transistor12. The emitter of transistor 12 is grounded and the collector thereofis connected through resistor 16 to +12 v. line 18. The value ofresistor 14 should be selected such that transistor 12 saturates so asto have a 60 Hz. inverted polarity square wave output at the collector.With the collector output connected to the lower end of the loadresistor 16, the output voltage, therefore, becomes negative, or lesspositive, relative to its previous positive value, when a positive inputsignal is fed to the base of transistor 12.

The collector is connected by lead 20 to the midpoint of a frequencydivider bistable flip-flop comprised of transistors 22 and 24 andassociated circuitry. The emitters of transistors 22 and 24 areconnected to a l2 v. line 25 and the bases and collectors arecross-connected through identical resistors 26. The midpoint, lead 20,is connected by capacitor 28 and resistor 30 in series to the collectorof transistor 22 and by capacitor 32 and resistor 34 in series tocollector of transistor 24. The junction between capacitor 28 andresistor 30 is also connected to transistor 22 base through steeringdiode 36 and the base is connected to lead 25 through resistor 38.Identical connections through steering diode 40 and resistor 42 aresupplied at the opposite side of the circuit. The diodes are oriented asshown with the positive terminals connected to the bases. With theoutput signal that appears at the collector of transistor 12 beingapplied simultaneously to transistors 22 and 24, the use of negativepulse steering diodes eliminates switching time delays. The collector oftransistor 22 is connected to the positive lead 18 through resistor 44and the collector of transistor 24 is connected through resistors 46 and48 in series to lead 18.

This flip-flop operates in conventional manner so that the inputfrequency is divided by two and a 30 Hz. square wave appears at thejunction between resistors 46 and 48. The remainder of the circuitselects the eleventh harmonic and perfonns a wave shaping function.

The junction between resistors 46 and 48 is connected through capacitors50 and 52 in series to the base of transistor 54. The base is alsoconnected to ground through resistor 56 and variable resistor 58 inseries. The emitter is connected to lead 25 through resistor 60 and thecollector to line 18 through load resistor 62.

The collector of transistor 54 is connected to the base of a secondtransistor 64 the emitter of which is connected to B+ lead 18 and thecollector to l2 v. line 25 through resistor 66. There is also a feedbackconnection from the collector of transistor 64 through resistor 68 backto the common point between capacitors 50 and 52 and a connection fromthe collector of transistor 64 through resistor 70 to the emitter ofcollector of transistor 64.

With appropriate values in this circuit to be given presently,

the input to transistor 54 acts as a high pass filter and the twotransistors act as an amplifier which because of the feedback pathstends almost to oscillate at the eleventh harmonic, 330 Hz., when thevariable resistor 58 is properly adjusted for maximum output voltage atthe mentioned frequency. The output from this portion of the circuitappears at lead 72 connected to the collector of transistor 64. Theactive filtered signal which appears at lead 72 is at the frequency of330 'Hz., however, modulated at 30 Hz. The pulsed wave train modulationpattern is free of quiescent regions and appears as a repetitious seriesof damped waves, wherein, the peaks decline in amplitude, with 11 cyclesper second present per modulation cycle.

The damped wave train at the proper frequency in lead 72 is connectedthrough resistors 74, 76 and 78 in series in that order to the base of atransistor 80. Resistor 76 is variable. The junction between resistors74 and 76 is connected to ground through resistor 82, and the base oftransistor 80 has a high frequency path to ground through capacitor 84.The input resistor-capacitor mesh to transistor 80, therefore, acts as alow pass filter and discriminates against frequencies above thefundamental at 330 Hz.

The emitter of transistor 80 is connected to lead 25 through resistor 86and the collector is connected to the lead 18 by resistor 88. Thecollector of transistor 80 is connected to the base of a second stagetransistor 90, the emitter of which is connected to line 18. Thecollector of transistor 90 is connected to output lead 92 and to line 25through resistor 94. Feedback paths are provided from the collector oftransistor 90 to the emitter of transistor 80 through resistor 97 andfrom the collector of transistor 90 through capacitor 96 to the midpointbetween resistors 76 and 78.

The circuit of transistors 80 and 90 is essentially similar to that oftransistors 54 and 64 excepting that the circuit of transistors 80' and90 emphasizes the 330 Hz. frequency and discriminates against spurioussignals at a frequency above 330 Hz. by attenuating at 12 db. per octavewhereas the cir cuit with transistors 54--64 emphasizes the 330 Hz.frequency and introduces some spurious higher frequencies in doing so.Resistor 76 is adjusted for maximum reliable signal output operationwith a minimum of resistance, which provides the desiredlocked-to-the-line coupling and the smoothest output wave at terminal92. The adjustable resistors 58 and 76 will adjust about the midpoint,for proper setting, with the related optimized RC components.

The circuit as so far described would give a good approximation of asine wave at line 92. Preferably, this is changed so as to produce someharmonic development, since the tone produced by such a signal is easierto tune to. This is accomplished by the resistor 100 and diode 98connected to ground. The diode shunts the signal at output 92 andproduces a nonsymmetrical wave. The value of the resistor can beselected as desired to produce a pleasing tone. Connected to thejunction formed by resistor 100 and diode 98 are two series resistors,101 and 102, which are also connected to ground. The resistors form avoltage divider with tenninal 93 taken between the resistors at therequired output voltage. The output terminal 93 with the 330 Hz. signalthereon may be connected to its own amplifier and speaker ofconventional design, or as usually will be the preferred arrangement, itcan be connected into the normally present guitar amplifier circuit soas to make use of the guitar amplifier and speaker.

The values of the components in the representative circuit shown anddiscussed are as follows:

' Transistors 64 and 90, type 2l l7 Other transistors, type 2108 Diodesl and 98, type 2603, and 36 and 40, type 2601 Resistors in ohms:

8 470 82 K L 1 66, 94 K 3. 9 16, 44, 46 K 5. 6

4, 78 K 22 100 K 33 60, 86 K 39 102 -K 47 76 K 50 38, 42 K 56 30, 34,58, 62, 88, 101 -K 100 26, 56 K 150 Capacitors in microfarads:

28, 32 (disc) 001 84 (mylar) 001 50, 52 075 96 47 The circuit describedin detail above divides the input 60 Although we prefer thisarrangement, it is also, of course, possible to take the eleventhharmonic of the input frequency and subsequently divide the resulting660 Hz. frequency by two and wave shape the resulting 330 Hz. E signalso as to obtain a similar end result. To accomplish this, FIG. 2, theinput essentially sine wave signal is saturated at 110, as in thetransistor 12 circuit in the previous embodiment. The saturated signalis fed into adynamic high pass filter 112 similar to the one shown at54, but adjusted to give a 660 Hz. signal modulated at 60 Hz. ratherthan 330 Hz. signalmodulated at 30 Hz. This 660 Hz. signal is applied toa pulsed clipper or trigger circuit 114 which may be of conventionaltype. The output from this circuit which has a steep wave front is fedto a bistable flip-flop 116, such as at 22-24 which divides thefrequency by two to give 330 Hz. which can be wave shaped as at 118 togive a signal at 120 substantially identical to that at 93.

Although it is not the primary objective, the circuit of FIG. 1 caneasily be converted to serve as a tuning reference when the availablepower line frequency is 50 Hz. rather than 60 Hz., thereby making thesystems as supplied for 60 Hz. useful in many countries where 50 Hz. isstandard. This is accomplished by converting the circuit to supply theseventh harmonic of 50 Hz. which is 350 Hz., very close to true musicalF at 349.228 Hz. To make the conversion it is necessary merely toinstall a connection between lead 20 and the junction between resistor46 and transistor 24 and to remove or disconnect load resistor 16. Notethat when lead 20 is connected to resistor 46, resistors 48 and 46 serveas the load in place of resistor 16. The connection from lead 20 throughresistor 46 to the input of transistor 54 bridges the frequency divider22-24 and the saturated 50 Hz. signal is, therefore, applied directly totransistor 54. The only other changes necessary are to adjust thesettings of resistors 58 and 76 to accommodate the higher frequency.

In making this adjustment, resistor 58 will be moved from approximatelyits midpoint to about one-third of its resistance value. This reducesthe total resistance 58+56 by ll.l percent. Resistor 76 is also adjustedto reduce its value similarly. These two adjustments take care of thefrequency increase of 6.06 percent (from 330 Hz. to 350 Hz.). Theportion of the circuit affected by this change is shown in FIG. 3 wherethe bridge across the frequency divider is indicated at 120 and resistor16 of FIG. 1 has been eliminated.

Of course, the elements of the frequency divider could be eliminatedfrom the circuit if the circuit is to operate from a 50 Hz. supply, butusually it is less expensive to make the systems all alike and convertthe few that are to be used where 50 Hz. is standard. If desirable, toaccommodate both standards, a single pole double throw switch 122, FIG.4, can be connected so that when in one position it connects lead 20 toresistor 16 for 60 Hz. and in the other position connects lead 20 tolead 120 for 50 Hz. Switches, not shown, can also be installed to switchin and out preset resistors of appropriate values at 58 and 76.

From the above it will be apparent that the system illustrated anddescribed provides an E signal at 330 Hz. for tuning purposes that is asprecisely regulated as is the 60 Hz. power circuit with which it isused. For all practical purposes they may be considered as absoluteregulation and is in fact more precise than most tuning standardscustomarily used. Also the system has the advantage of being easilyconvertible for operation on 50 Hz. standard frequency.

Having described the invention what I claim is:

1. A circuit for providing a musical instrument tuning reference signalcomprising circuit means for receiving the standard alternating currentpower line frequency at 60 Hz., means for dividing said powerlinefrequency by two to provide a signal at 30 Hz. said dividing meansacting on said signal to provide said 30 Hz. signal with a series of oddharmonics, and means for extracting the eleventh hannonic from saiddividing means signal to provide a tuning reference musical E signal at330 Hz.

2. The circuit of claim 1 in which the means for extracting the eleventhharmonic is a feedback amplifier conditioned so as almost to oscillateat 330 Hz.

3. The circuit of claim 1 in which said dividing means is a bistableflip-flop.

4. The circuit of claim 3 in which the means for extracting the eleventhharmonic is a feedback amplifier conditioned so as almost to oscillateat 330 Hz.

5. The circuit of claim 1 including means for distorting said 330 Hz.signal to add a series of even and odd harmonics thereto.

6. The circuit of claim 5 in which the means for extracting the eleventhharmonic is a feedback amplifier conditioned so as almost to oscillateat 330 Hz.

7. The circuit of claim 5 in which the distorting means is a diode.

8. The circuit of claim 7 in which the means for extracting the eleventhharmonic is a feedback amplifier conditioned so as almost to oscillateat 330 Hz.

9.. The circuit of claim 5 in which said dividing means is a bistableflip-flop.

10. The circuit of claim 9 in which the means for extracting theeleventh harmonic is a feedback amplifier conditioned so as almost tooscillate at 330 Hz.

11. The circuit of claim 9 in which the distorting means is a diode.

12. The circuit of claim 11 in which the means for extracting theeleventh harmonic is a feedback amplifier conditioned so as almost tooscillate at 330 Hz.

13. A circuit for providing a musical instrument tuning reference signalcomprising an input for receiving a standard alternating currentpowerline frequency, and means responsive to said frequency for adding aharmonic series to said input frequency and harmonic selecting means toprovide an output signal at a selected harmonic of the input signalwhich selected harmonic is at substantially the fundamental frequency ofa note of the musical scale.

14. The circuit of claim 13 in which the means for adding a harmonicseries is a saturated amplifier.

15. The circuit of claim 13 in which the harmonic selecting means is afeedback amplifier having tuning means to condition said amplifieralmost to oscillate at a selected frequency in the range between 330 Hz.and 350 Hz.

16. The circuit of claim 13 in'which the harmonic selecting means is afeedback amplifier conditioned so as almost to oscillate at 660 Hz.

17. The circuit of claim 16 including means for dividing the frequencyof the signal from said feedback amplifier by two.

18. The circuit of claim 13 in which the input frequency is 50 Hz. andthe harmonic selecting means selects the seventh harmonic.

19. The circuit of claim 18 in which the means for adding a harmonicseries is a saturated amplifier.

20. The circuit of claim 18 in which the harmonic selecting means is afeedback amplifier conditioned so as almost to oscillate at 350 Hz.

1. A circuit for providing a musical instrument tuning reference signalcomprising circuit means for receiving the standard alternating currentpower line frequency at 60 Hz., means for dividing said powerlinefrequency by two to provide a signal at 30 Hz. said dividing meansacting on said signal to provide said 30 Hz. signal with a series of oddharmonics, and means for extracting the eleventh harmonic from saiddividing means signal to provide a tuning reference musical E signal at330 Hz.
 2. The circuit of claim 1 in which the means for extracting theeleventh harmonic is a feedback amplifier conditioned so as almost tooscillate at 330 Hz.
 3. The circuit of claim 1 in which said dividingmeans is a bistable flip-flop.
 4. The circuit of claim 3 in which themeans for extracting the eleventh harmonic is a feedback amplifierconditioned so as almost to oscillate at 330 Hz.
 5. The circuit of claim1 including means for distorting said 330 Hz. signal to add a series ofeven and odd harmonics thereto.
 6. The circuit of claim 5 in which themeans for extracting the eleventh harmonic is a feedback amplifierconditioned so as almost to oscillate at 330 Hz.
 7. The circuit of claim5 in which the distorting means is a diode.
 8. The circuit of claim 7 inwhich the means for extracting the eleventh harmonic is a feedbackamplifier conditioned so as almost to oscillate at 330 Hz.
 9. Thecircuit of claim 5 in which said dividing means is a bistable flip-flop.10. The circuit of claim 9 in which the means for extracting theeleventh harmonic is a feedback amplifier conditioned so as almost tooscillate at 330 Hz.
 11. The circuit of claim 9 in which the distortingmeans is a diode.
 12. The circuit of claim 11 in which the means forextracting the eleventh harmonic is a feedback amplifier conditioned soas almost to oscillate at 330 Hz.
 13. A circuit for providing a musicalinstrument tuning reference signal comprising an input for receiving astandard alternating current powerline frequency, and means responsiveto said frequency for adding a harmonic series to said input frequencyand harmonic selecting means to provide an output signal at a selectedharmonic of the input signal which selected harmonic is at substantiallythe fundamental frequency of a note of the musical scale.
 14. Thecircuit of claim 13 in which the means for adding a harmonic series is asaturated amplifier.
 15. The circuit of claim 13 in which the harmonicselecting means is a feedback amplifier having tuning means to conditionsaid amplifier almost to oscillate at a selected frequency in the rangebetween 330 Hz. and 350 Hz.
 16. The circuit of claim 13 in which theharmonic selecting means is a feedback amplifier conditioned so asalmost to oscillate at 660 Hz.
 17. The circuit of claim 16 includingmeans for dividing the frequency of the signal from said feedbackamplifier by two.
 18. The circuit of claim 13 in which the inputfrequency is 50 Hz. and the harmonic selecting means selects the seventhharmonic.
 19. The circuit of claim 18 in which the means for adding aharmonic series is a saturated amplifier.
 20. The circuit of claim 18 inwhich the harmonic selecting means is a feedback amplifier conditionedso as almost to oscillate at 350 Hz.